Good. As soon as I get my ATmega168 with the Arduino bootloader burned, I am going to work in a project to use TM751 transceiver's daughter board as a universal wireless receiver. I already did it with a PIC12F629.

CM17A and TM751 daughter board with Arduino is the perfect and complete X10 wireless solution.

Nice work! Minor typo, you have GND on the DB9 going to pin 4, I believe you mean 5? Anyway, that works for me!

Note that the Firecracker has both a female and male side. The female side is the one meant to plug in the PC, that's the side I used as the input, and pin 1 is on the upper right, with pin 5 going to the left. Might not be so obvious if you don't have a PC right in front of you!.

This is a better (and cheaper) solution than the older X10 arduino library using the TW523 unit (actually I had the 1132b). I wasn't able to get that working reliably.

jcgalvezv, this comment re the TM751 is intriguing. If I understand correctly, you want to open a TM751, and use the daughterboard along with the Firecracker as an RF link. You're not really intending to use X-10 at all?

I can see why this could work, but why is it desirable? Why not use one of the RX433/TX434 family, or Zigbee or Bluetooth? It's not like X10 component reliability or quality anything to write home about, and I don't think it would be cheaper than '433 family and it certainly wouldn't approach the reliability of the latter, I would think.

I must be missing some advantage - I have several TM751s so if there's a cool use for them I'm overlooking, I'm interested!

jcgalvezv, this comment re the TM751 is intriguing. If I understand correctly, you want to open a TM751, and use the daughterboard along with the Firecracker as an RF link. You're not really intending to use X-10 at all?

No, I want to have a completely wireless X10 system. Firecracker to send commands and TM751 daughter board to receive commands sent from all the motion sensors and remote controls directly to the microcontroller. TM751 daughter board has the capability to receive commands from all the house codes.

a digital volume control for hifi/stereo using a lcd display, IR receiver, rotary encoder, PGA style volume control chip and some input/output device select relays.

the x10/firecracker thing was unexpected but now, when I switch off a main speaker amp and switch on my dedicated headphones amp (yes, they are 2 different boxes) I can power the unused one down via x10 devices and power the other one up the same way (via another device address).

your code came in useful - and it took all of 5 minutes to solder into a spare firecracker (I had no db9's) and download your code to test it. when I heard a relay CLICK! loud in the other room, I knew it was working